1. Technical Field
This invention relates to apparatus and methods for re-shaping the backing plates of rotary drum brake cores in the making of re-manufactured brake shoes.
2. Related Prior Art
Rotary drum-type brake shoes are formed by bonding a lining of friction material such as asbestos or the like to the convex outer surface of a metal backing plate of the brake core. Extending from the opposite concave inner surface of the backing plate are a set of laterally spaced mounting brackets for securing the shoes to the associated calipers of the brake system.
Over time, the lining is caused to wear to the point where the brake shoes need to be replaced. It is quite common to reclaim the metal core of spent brake shoes and use them to produce remanufactured brake shoes. The remanufacturing process involves stripping the old liner from the core, reshaping the backing plate to correct any warpage that may have occurred in service from prolonged exposure to extreme temperature changes and high pressure conditions, and applying a new lining to the reshaped core.
Presently, the backing plates are reshaped via a coining operation in which the convex outer surface of the backing plate is cradled by complementary concave working surface of a fixed lower die of a coining press. An upper movable die of the press supports a pair of die inserts or tools having lower convex working surfaces that compliment the concave inner surface of the backing plate. The die inserts are spaced laterally from one another by a distance sufficient to straddle the mounting brackets of the core. In operation, the backing plate is struck with great force by the upper die inserts, causing the side regions of the backing plate to either side of the mounting brackets to be reshaped to the proper configuration.
One inherent disadvantage of the present tooling and reshaping process is that the middle region of the backing plate located between the mounting brackets is not acted upon by the tooling and thus does not get reshaped in the process. Consequently, there is no assurance that the middle region of the backing plate is true to shape following the current coining operation.
According to the invention, a coining die apparatus and method is provided for reshaping metal brake shoe cores in the production of remanufactured rotary drum brake shoes of the type in which the metal core includes an arcuate metal backing plate having a convex outer surface for receiving a bonded friction liner, and an opposite concave inner surface from which a pair of laterally spaced mounting brackets extend for mounting the core to an associated brake system.
The apparatus includes a set of opposing dies that are movable relative to one another to impart a coining force on a backing plate disposed therebetween. One of the dies includes a concave working surface configured to support the convex outer surface of the backing plate. The other die set includes a pair. of outer die portions having convex working surfaces corresponding in shape and size to the convex outer surface of the backing plate. The outer die portions are spaced laterally from one another by a distance sufficient to receive the mounting brackets therebetween when the dies are closed, with the outer die portions forcibly engaging and reshaping corresponding outer regions of the backing plate on either side of the mounting brackets. According to a characterizing feature of the invention, the other die set further includes a middle die portion disposed between the adjacent outer die portions and having a convex working surface. The middle die portion is spaced laterally from the adjacent outer die portions providing a gap between the middle die portion and each of the outer die portions for receiving the mounting brackets therein when the dies are closed, thereby enabling the middle die portion to forcibly engage and reshape a corresponding middle region of the backing plate located between the mounting brackets.
According to a method of the invention, the backing plate of a metal brake core of a rotary drum brake shoe is reshaped in a press having relatively movable first and second dies by supporting a convex outer surface of the backing plate against a corresponding concave working surface of the first die. The second die set is provided with a pair of outer die portions having convex working surfaces spaced laterally from one another by a distance sufficient to receive the mounting brackets therebetween. The second die set further includes a middle die portion disposed between the outer die portions and having a convex working surface. The middle portion is spaced laterally from the adjacent outer die portions to provide a gap between the middle portion and each of the outer die portions sized to receive the mounting brackets therein. The method includes closing the dies with force such that the mounting brackets are received in the gaps between the outer and middle die portions, while the outer die portions forcibly engage and reshape corresponding side regions of the backing plate on either side of the mounting brackets and the middle portion extends between the mounting brackets and forcibly engages and reshapes a corresponding middle region of the backing plate located between the mounting brackets.
According to a further aspect of the invention, a method is provided for modifying an existing brake core coining die used for reshaping the metal backing plate of a rotary drum brake core in a remanufacturing operation of the type in which the backing plate has a convex outer surface for receiving a bonded friction liner and an opposite concave inner surface from which a pair of laterally spaced mounting brackets extend for mounting on a brake actuating system. The coining die to be modified is of the type including relatively movable dies, one of which presents a concave working surface for engaging the convex outer surface of the backing plate, and the other of which includes a pair of outer die portions spaced laterally from one another by a distance sufficient to receive the mounting brackets therebetween and having convex working surfaces which forcibly engage and reshape corresponding side regions of the backing plate adjacent either side of the mounting brackets, with there being a middle region of the backing plate located between the brackets which is not engaged by the outer die portions and consequently not reshaped. According to the invention, such a coining die is modified by disposing a middle die portion in the space between the two outer die portions. The middle die portion has a convex working surface and is spaced from the adjacent outer die portions in such manner as to provide a gap between the middle die portion and each of the adjacent outer die portions to accommodate the mounting brackets therein when the dies are closed, such that the middle die portion enters between the brackets and forcibly engages and reshapes the middle region of the backing plate simultaneously with the reshaping of the side regions.
The invention has the advantage of providing a simple, low cost apparatus and method for reshaping the entire backing plate of a rotary drum brake core, including the middle region between the mounting brackets. In this way, it is assured that any warpage that may have occurred in the middle region as a result of previous service is corrected during the remanufacturing process before application of the new friction liner.
The invention has the further advantage of improving the quality assurance of remanufactured rotary drum brake shoes by simply modifying existing coining apparatus in a manner that enables the middle region of brake core backing plates to be simultaneously reshaped with the side regions of the backing plates.